class_docstr: FastAI callback integration.
  Pass an instance of this class to FastAI learner as argument ``cbs``.
  FastAI will call relavent mehtods of this class to log metrics.
code: def after_batch(self):
      tracker.add_global_step()
      if self.training:
          metrics = {"loss.train": self.learn.loss}
      else:
          metrics = {"loss.valid": self.learn.loss}
      try:
          for m in self.learn.metrics:
              if m.value is not None:
                  metrics[m.name] = m.value
      except:
          pass
  
      tracker.save(metrics)
  
file_path: labml/client/labml/utils/fastai.py
imports: from fastai.callback.core import Callback, patch
  from fastai.learner import Learner
  from labml import tracker
label_desc: Use image node_id 3 for calling the LabMLFastAICallback obj's underlying member method code with example usage: obj.after_batch() without return types